llvm dev - May 2020 - Cast between struct

Dear All,

In my development, a function returns a struct {i8*, i64}, and on the
call site I need to assign the return value to a struct of type {some_struct*,
i64}.
One way to do it is to call the mutateType() method of llvm::Value on
the return value of the function call; however, I’m concerned that this
mutateType()
method might be too disruptive (it’s discouraged to use it by the
documentation).
Since LLVM does not support cast between structs. Is there any way I can safely
“cast” a value of one struct type to another?

Thanks,
- Jie

You can
1. extract individual elements of {i8*, i64},
2. bitcast the first to some_struct*,
3. insert them into a new struct of type {some_struct*, i64}.


--
Krzysztof Parzyszek  kparzysz at quicinc.com   AI tools development
> -----Original Message-----
> From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Jie
Zhou via
> llvm-dev
> Sent: Wednesday, May 6, 2020 7:17 PM
> To: Joerg Sonnenberger via llvm-dev <llvm-dev at lists.llvm.org>
> Subject: [EXT] [llvm-dev] Cast between struct
>
> Dear All,
>
> In my development, a function returns a struct {i8*, i64}, and on the call
> site I need to assign the return value to a struct of type {some_struct*,
> i64}.
> One way to do it is to call the mutateType() method of llvm::Value on the
> return value of the function call; however, I’m concerned that this
> mutateType() method might be too disruptive (it’s discouraged to use it by
> the documentation).
> Since LLVM does not support cast between structs. Is there any way I can
> safely “cast” a value of one struct type to another?
>
> Thanks,
> - Jie
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

> On May 6, 2020, at 21:53, Krzysztof Parzyszek <kparzysz at
quicinc.com> wrote:
> 
> You can
> 1. extract individual elements of {i8*, i64},
> 2. bitcast the first to some_struct*,
> 3. insert them into a new struct of type {some_struct*, i64}.
Thanks for the help. I’m thinking the same way. Now I’m stuck with
how to create a struct; I know how to create a llvm::StructType but
I’m not clear of how to create a Value whose type is struct). It seems that
llvm disallowed directly create a Value object; all Values are created from
one of its numerous descendants. Can you give me some guidance here?

Thanks,
- Jie
> 
> 
> --
> Krzysztof Parzyszek  kparzysz at quicinc.com   AI tools development
> 
>> -----Original Message-----
>> From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of
Jie Zhou via
>> llvm-dev
>> Sent: Wednesday, May 6, 2020 7:17 PM
>> To: Joerg Sonnenberger via llvm-dev <llvm-dev at lists.llvm.org>
>> Subject: [EXT] [llvm-dev] Cast between struct
>> 
>> Dear All,
>> 
>> In my development, a function returns a struct {i8*, i64}, and on the
call
>> site I need to assign the return value to a struct of type
{some_struct*,
>> i64}.
>> One way to do it is to call the mutateType() method of llvm::Value on
the
>> return value of the function call; however, I’m concerned that this
>> mutateType() method might be too disruptive (it’s discouraged to use it
by
>> the documentation).
>> Since LLVM does not support cast between structs. Is there any way I
can
>> safely “cast” a value of one struct type to another?
>> 
>> Thanks,
>> - Jie
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>>
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